Spark plug



April 18, 1944. s. D. HERON SPARK PLUG Filed Aug. 12, 1942 INVENTQR 6' 4?. WM

ATTORNEY der in the core.

Patented Apr. 18, 1944 2,347,050 srsan PLUG Sam'D. Heron, Detroit, Micln, assignor of onehalf to Ethyl Corporation, Detroit, Mich a corporation of Delaware, and one-half to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Application August 12. 1942, Serial No. 454,601

2 Claims.

This invention relates to a construction of a spark plug core and its center electrode and a mode of sealing and fastening the electrode in the core. While the invention is useful for any type of internal combustion engine it finds its greatest utility in very high power output engines where the working pressures are high and the internal mechanical stresses in the spark plug are large.

Heretofore it has been proposed. to fasten the center electrode in the core by inserting a; powder such as talc between the two and highly compressing the powder'so that it forms a binder and seal. In some of these constructions a stepped bore in the core is used, the electrode has a raised shoulder and the powder is compressed behind the shoulder on the electrode holding this shoulder against the internal shoul- In most of these constructions the electrode is inserted into the bore in the core from the outer end of the core, 1. e., the endof the spark plug which is outside the engine cylinder. Where a stepped bore is employed the larger bore faces the outer end of the spark plug; Such constructions have the inherent defect that the gas pressure in the engine is working against the seal between the electrode and the core tending to loosen it. The many constructions shown in the prior art are evidence of the diificulties in= volved in trying to make a good seal with this form of construction.

In the present invention a stepped bore is used with the larger bore facing the inner end of the spark plug. The electrode is also stepped, and it is inserted into the core from the inner end. A compressible or compactible binding material is inserted in the bottom of the larger-bore and sufilcient pressure applied so that the binding material seals and holds the electrode in position in the core.

The single figure shows my form of core and electrode construction and also shows a preferred shape of core to be used when the larger bore faces the inner end of the core. The size of the parts as shown is three times the size as now used in an aviation spark plug.

In the drawing in which the parts are shown in longitudinal section except for the center electrode, It is the core, made of a suitable insulating material, having a small bore H facing the outer nd of the core, a larger bore l2 facing the inner end of the core and a shoulder I3 where the two bores meet. The electrode H has a larger inner end seated in the larger bore l2 and a reduced portion I6 passing through the small bore H to iii the outer end where contact with the i tion wire is made. There is a shoulder H on the electrode. Near the outer end of the spark plug core the bore is enlarged to receive a metal sleeve l8 which surround the small end of-the electrode. The enlarged end of this sleeve increases the surface on which the ignition wire connector makes contact.

In the bottom of the larger bore is the compressed binding and sealing substance l9. This material is compacted by axial pressure on the large end of the electrode. In aviation plugs I have used a pressure of five hundred pounds. This substance may be a granular material such as talc, steatite, etc., which is inserted by pourm it in or it may be a small cylinder of metal or it may be a cylinder of asbestos twine. If a granular material is used it may be preformed as by pressure or by the use of a cement into a small cylinder which can readily be slipped into the core, the cylinder being crushed and the granular material forced into a tight binding relation with the core and electrode by high pressure on the large end of the electrode. The preformed metal cylinder will be flattened and enlarged when pressure is applied axially to the large 'end of the electrode forcing the cylinder into firm contact with the walls of the electrode and core.

Words such as compacting andcompacted are used in the claims to include compressing a 'material until it is deformed. This deformation need not be great because the preformed cylinders may be made substantially in their final size and shape so that their deformation under pressure is small.

The gas pressure within the engine acts against the large end or the electrode. The working pressure is high in engines of high power output used for commercial and military aviation and tends to maintain the seal rather than disrupt it. As

a result of this more attention can now be given to the. selection of materials for their scaling properties and so widen the field of materials which may be used and of methods for completing the electrode-core assembly.

The spark plug core illustrated has an external conical seating surface extending from A to B with the large end of the cone on the inner end of'the spark plug. I prefer this form of core with the stepped bore shown because the backing provided by the metal shell of the spark plug over the extended area A--B gives ensurance against breakage, particularly in spark plugs working under high pressure with resultant high internal mechanical stresses. This core is backedhy the spark plug shell over the enlarged conical surface A-B and the remainder of the core is mailer and preferably cylindrical so that it can readily he slipped into a spark plug shell from the inner end. While this is my preferred form of core the use of the stepped bore as described is not limited to this form of core and may be used with an desired core shape.

I claim: I

1. A spark plug core having a stepped bore, the larger bore facing the inner end oi the core, a stepped electrode having 1e large end in the large bore and it small end in the small bore core.

SAM D. HERON. 

